Process for the concentration of nitric acid



0. JENSEN.

PROCESS FOR THE CONCENTRATION OF NITRIC ACID.

APPLICATION FILED FEB. 24, 1920.

Patented Nova 1, 1.921.

Tau-Pr JiNQs UNITED STATES rarENT OFFICE.

OLA]? JENSEN, OF NOTODDEN, NORWAY, ASSIGNOR T0 NORSK HYDRO-ELEKTRISK KVAELSTOFAKTIESELSKAB, 0F OHRISTIANIA, NORWAY.

PROCESS FOR THE CONCENTRATION or NITRIC ACID.

T 0 all whom it may concern.

Be it known that LOLAF JENSEN, a subject of the King of Norway, residing at Notoddeu, Norway, have invented certain new and useful Improvements in Processes for the Concentration of Nitric Acid; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same, reference being had to the accompanying drawings, and to letters or figures of reference marked thereon, which form a part of this specification.

This invention relates to the concentra tion of nitric acid by passing vapors of dilute nitric acid in contact with concentrated sulfuric acid and has for its object an improved method of carrying such concentration into effect, whereby certain drawbacks connected with the process as hitherto practised are avoided.

Vhen nitric acid is concentrated in accordance with the recent methods by converting the acid into vapor and desiccating the vapor by means of sulfuric acid difiiculties involved by the formation of scale are met with. The nitriciacid never is of such a high degree of purity as to be quite free from non-volatile constituents. Experience shows that such solid constituents of the acid are precipitated upon the walls forming scale, which even when present in a very thin layer will effect a considerable disturbance of the transmission of heat. According to the observations which I have made it is possible, however, to eliminate this drawback by a change in the conditions of working. The concentration has hitherto been practised by introducing the dilute nitric acid into an evaporator, in which the volatile constituents have been converted into vapor, while the solid constituents are retained, and when the concentration as to solid constituents ha increased to the point of saturation, the solids will be precipitated at the points where the evaporation takes place, that is at the heating surface.

According to the present invention the process is carried into eflect under such conditions that the precipitated ubstances are prevented from forming scale by adhering to the surfaces of the apparatus.

This result is attained by only partially evaporating the acid, maintaining the acid Specification of Letters Patent.

Patented Nov. 1, 1921.

Application filed February 24, 1920. Serial No. 360,818.

in motion during the evaporation and canslng the separation of precipitated solid substances outside of the evaporator.

In carrying the process into effect a quantity of acid in excess of that which is to be evaporated is passed through the evaporator. This excess quantity of acid is suitably lntroduced into the evaporator again after having beenfreed from sludge in a clarifien,

The clarifier as Well as the conduits to and from the ame may be insulated whereby the losses of heat can be made quite insignificant. When the percentage of solid impurlties is quite small, it is not necessary to provide a constant clarifying of the entire quantity of acid in circulation. One may for instance proceed by passing only a minor part of the circulation liquid through the clarifier. I

In the following a method of carrying the invention into effect is described with reference to the accompanying drawing, which is a sectional view of a concentration plant. In the illustrated example A designates a boihng or evaporation column provided with steam jacket, into which steam is sup plied at a, water of condensation being discharged at 6. From the inner tube of the column the vapor enters the separator B, where the particles of liquid are separated out. The liquid then passes through the pipe 0 to the sludge collector C and therefrom back to the inner tube in the column A. From the sludge collector the sludge is discharged periodically through the valves (Z and 6, fresh quantities of acid being supplied through the pipe f.

The nitric acidvapor from the separator B enters the tower D, where it meets a flow of concentrated sulfuric acid which trickles down through a layer of pieces of O1aims 1. The process of concentratm nitric acid, which comprises circulating t e crude nitric acid through an evaporator, withdrawing. nitric acld vapor -from the circula'ting current of acid, and drying said "vapor.

2. The process of concentratm mtric acid, which comprises circulating t e crude nitric acid throu h an evaporator and a sludge chamber, w ereby the solids are separated outside the evaporator in said sludge chamber, and withdrawing and drying the nitric acid vapors.

3,. The process of concentrating 7 Witnesses:

acid, which comprises circulating the crude nitric acid through an evaporator, a. liquid separator and a sludge chamber, whereby.

the solids are separated 'outside the evaporator in said sludge chamber, and withdrawing nitric acid va ore from the separator, and drying the nitric acid vapors.

OLAF JENSEN.

E. S. I'IENDRIOKBEN, ROBERT H. 

